A conventional X-ray tube apparatus, as shown in FIG. 4, includes a cathode 105 which releases electrons (also called thermion or electron beams), deflection coils 106 which deflect the electrons released from the cathode 105, a target 107 which generates X-rays (with sign xr in FIG. 4) by allowing the electrons deflected by the deflection coils 106 to bombard on its disk peripheries (see Patent Document 1, for example). An envelope rotation type X-ray tube 101 has an envelope 102 rotatable about a rotation center line R with the target 107. The target 107 is an anode.
A tube voltage is applied between the cathode 105 and the target 107 which is an anode. The tube voltage is a voltage for accelerating the electrons released from the cathode 105. An amount of deflection of the electrons deflected by the deflection coils 106 depends on the tube voltage. Therefore, in order to keep constant focal positions for causing the electrons to bombard on positions of the target 107 set beforehand and generate X-rays, an amount of current flowing to the deflection coils 106 is controlled according to variations in the tube voltage.
Patent Document 2 discloses a construction for capturing recoil electrons, among electrons having bombarded on a rotating anode target, which repeat scattering without being converted into heat or X-rays.